1. Field of the Invention
This invention relates to a device and method for mixing mortar or the like, and more particularly to a mixing device capable of effectively stirring and mixing pulverulent materials such as cement with water by rotating screw blades while serving aggregate contained in the pulverulent materials as a mixing agitator like milling balls in a ball mill.
2. Description of the Prior Art
For example, in a case of making ready-mixed concrete, if raw materials such as cement and aggregate are mixed with water at one time, desirable cement paste cannot be obtained nor solidified intensely because the cement and aggregate will not be uniformly dispersed in the cement paste. The cement in the form of fine pulverulent particles tends to gather in the water to form lumps which are immiscible with the water. The finer the pulverulent particles are which are to be mixed with water having surface tension, the easier such immiscible lumps of the pulverulent particles occur. The surface tension of the water acts on air accommodated in the lumps of the particles, such that the lumps of the particles become difficult to break.
As typical mixers of this type, there have been so far practically used a forced stirring type pan mixer, a horizontally biaxial mixer, and a tilting mixer with a rotary drum. Each of these conventional mixer is provided with a mixing blade or rotary drum as a mixing agitator means which is rotated at a low speed to break the aforenoted lumps of pulverulent particles formed in a mixture paste.
However, since such conventional mixers generally adopt a stirring mechanism utilizing gravity, aggregate mixed in the mixture paste cannot bring about an agitating action as exerted by milling balls used in a ball mill (ball mill effect) because of large absorbed energy of water in the mixture paste. Thus, the conventional mixers are restricted in their ability to agitate the mixture paste. Accordingly, with the conventional mixers as noted above, theoretically, the aforementioned agitator means must be driven at a high speed of rotation for a long time in order to impart kinetic energy to the aggregate in the mixture. However, the mixture paste will be rotated while sticking to the rotating agitator means or scattered away without being stirred when the agitator means is rotated at a high speed. For that reason, in the conventional mixer, the mixture paste cannot be agitated at a high speed as a matter of course, so that the raw materials cannot be mixed sufficiently and dispersed uniformly in the mixture paste resultantly obtained.
As one attempt to effectively mix cement and aggregate with water, Japanese Patent Publication SHO 61-7928(B) has proposed a step mixing device in which cement is initially mixed with water to obtain cement paste as an intermediate, so that aggregate such as sand can be mixed with the cement paste thus obtained by using another mixer. However, with this conventional mixing device, lumps of cement which are immiscible with water are inevitably formed in the mixture and cannot be effectively broken and dispersed uniformly in the mixture, because air accommodated in the lumps of cement serves as a cushion when the agitator is rotated slowly or because of other possible reasons.
Various studies have been made by the inventors on how kinetic energy for effectively breaking the lumps of pulverulent materials such as cement can be introduced into a mixture paste to uniformly disperse the pulverulent materials in the mixture paste.
From the results of the studies made by the inventors, it was first confirmed that it is desirable to exert kinetic energy directly to fine aggregate such as sand in order to completely break the lumps of the pulverulent materials which are immiscible with water by an agitating action brought about by the aggregate like milling balls contained in a ball mill. The "mortar" herein is obtained by uniformly dispersing inert fine aggregate (sand and the like) and active binding materials (mixture of fine powdered particles such as cement clinker, silica, blast furnace slag, and fly ash, which react with water or chemical solution) in water and mixing agents. Therefore, by driving the agitator of a mixer at a high speed to impart kinetic energy to the lumps of the pulverulent materials and fine aggregate in the mixture, the aggregate can collide with the lumps of the pulverulent materials, resulting in introduction of the kinetic energy into the lumps of the pulverulent materials which are immiscible with water. Thus, the aggregate in the mixture stirred at high speed can be practically used instead of the milling balls used in the ball mill.
Secondly, the mixture paste cannot easily be prevented from being rotated with the rotary agitator means such as a mixing blade or drum driven at a high speed nor from being scattered away when using the mechanism of the conventional mixer in which only the drum or single mixing blade is rotated. The inventors have found a solution to easily and properly mix such pulverulent materials with water by driving two rotary agitating members at a high speed. The rotary agitating members are disposed one on another and rotated at high speed so as to cause the mixture paste of the pulverulent materials and water to move fast in between the opposed agitating members. In the region between the rotating agitating members, the mixture paste flows rapidly and is compressed. Under the high pressure brought about by the rapid current of the mixture paste between the agitating members, the aggregate functions as the milling balls used in the ball mill.
Thirdly, it was further found that the particles of the fine aggregate in the mixture paste discharged from between the opposed agitating members act on the lumps of the pulverulent material which remain static in a mixing container. This is because the particles of the fine aggregate paste rapidly flowing out from between the agitating members are caused to rush into the mixture paste moving around in the mixing container.